It is known to provide a transportation vehicle which traverses a roadway as shown in U.S. Pat. No. 3,312,180, where guide wheels depend below the vehicle and engage a guide beam supported between and extending parallel to spaced vehicle support tracks. Electric power has been supplied to the vehicle through suitable power collectors operative with power supply rails mounted parallel to the guide beam and extending along the roadway tracks. It is known to support each collector shoe by a parallelogram arrangement carried by the vehicle as it moves along the roadway with a spring member providing desired contact pressure for the collector shoe against the associated power rail as shown in U.S. Pat. No. 4,168,770.